1. Field of the Invention
The technical field relates to a display device and a driving method thereof. In particular, the technical field relates to a display device including a photosensor and a driving method thereof. Further, the technical field relates to a semiconductor device and a driving method thereof.
2. Description of the Related Art
In recent years, a display device provided with a touch sensor has attracted attention. The display device provided with a touch sensor is called a touch panel, a touch screen, or the like (hereinafter referred to simply as a touch panel). Examples of the touch sensor include a resistive touch sensor, a capacitive touch sensor, and an optical touch sensor which are different in operation principle. With the touch sensor, an object (e.g., a pen and a finger) touching a display device can be detected. Therefore, data for controlling the display device can be input by the use of the touch sensor as an input device. In addition, a display device including an optical touch sensor can be also used as a contact area sensor (e.g., Patent Document 1).
Further, as an example of a device without a display panel, a semiconductor device such as an image sensor can be given.